Low permeability airbag cushions having extremely low silicone-based coating levels

ABSTRACT

Coated inflatable fabrics and more particularly concerns airbag cushions to which very low add-on amounts of silicone-based coating have been applied and which exhibit extremely low air permeability are provided. The inventive inflatable fabrics are primarily for use in automotive restraint cushions that require low permeability characteristics (such as side curtain airbags). Traditionally, heavy, and thus expensive, coatings of compounds such as neoprene, silicones, and the like, have been utilized to provide such required low permeability. The inventive fabric utilizes an inexpensive, very thin, substantially uniform silicone coating to provide such necessarily low permeability levels. Thus, the inventive coating comprises at least a single layer comprising a majority of silicone-based material, wherein the total thickness of the single layer is at most about 3.0 ounces per square yard as applied to a target fabric surface. The inventive airbag exhibits a characteristically long leak-down rate as compared to other coated airbags.

FIELD OF THE INVENTION

This invention relates generally to coated inflatable fabrics and moreparticularly concerns airbag cushions to which very low add-on amountsof silicone-based coating have been applied and which exhibit extremelylow air permeability. The inventive inflatable fabrics are primarily foruse in automotive restraint cushions that require low permeabilitycharacteristics (such as side curtain airbags). Traditionally, heavy,and thus expensive, coatings of compounds such as neoprene, silicones,and the like, have been utilized to provide such required lowpermeability. The inventive fabric utilizes an inexpensive, very thin,substantially uniform silicone coating to provide such necessarily lowpermeability levels. Thus, the inventive coating comprises at least asingle layer comprising a majority of silicone-based material, whereinthe total thickness of the single layer is at most about 3.0 ounces persquare yard as applied to a target fabric surface. The inventive airbagexhibits a characteristically long leak-down rate as compared to othercoated airbags.

BACKGROUND OF THE PRIOR ART

Airbags for motor vehicles are known and have been used for asubstantial period of time. A typical construction material for airbagshas been a polyester or nylon fabric, coated with an elastomer such asneoprene, or silicone. The fabric used in such bags is typically a wovenfabric formed from synthetic yarn by practices that are well known inthe art.

The coated material has found acceptance because it acts as animpermeable barrier to the inflation medium. This inflation medium isgenerally a gas generated from a gas generator or inflator. Such gas isconveyed into the cushion at a relatively warm temperature. The coatingobstructs the permeation of the fabric by such hot gas, therebypermitting the cushion to rapidly inflate without undue decompressionduring a collision event.

Airbags may also be formed from uncoated fabric which has been woven ina manner that creates a product possessing low permeability or fromfabric that has undergone treatment such as calendaring to reducepermeability. Fabrics which reduce air permeability by calendaring orother mechanical treatments after weaving are disclosed in U.S. Pat.Nos. 4,921,735; 4,977,016; and 5,073,418 (all incorporated herein byreference).

Traditional silicone coatings have proven ineffective at low add-oncoating weights over target airbag fabric surfaces for low permeabilitycharacteristics. Typically, such coatings have required extremely thicklayers of materials to provide the desired low permeability levelsrequired for long-term rollover protection situations (particularly forside-curtain airbags). In general, past silicone-based coatings haveutilized non-solvent- and solvent-based compositions having dry coatingweights for such silicones above 3 and approaching lower levels of atleast 4 ounces per square yard for both the front and back panels ofside curtain airbags. As will be appreciated by one of ordinary skill inthis art, high add-on weights substantially increase the cost of thebase fabric for the airbag and make packing within small airbag modulesvery difficult. Furthermore, traditionally utilized silicones exhibitvery low tensile strength and elongation at break characteristics thatdo not withstand high pressure inflation easily without the utilizationof very thick coatings. However, silicones provide excellent durability,aging, and processability benefits, which, if provided with extremelylow add-on compositions, would translate into highly desirable airbagcoatings. Additionally, as noted in greater detail below, the productionof integrally woven side curtain airbags has eliminated the possibilityof coating on both the front and back sides of individual fabric panels.As such, there is a greater need to accord relatively thin coatinglayers on solely the outside panels (i.e., front) of such articles. Todate, the ability to restrict coatings to low levels of silicone-basedmaterials has been unavailable.

The use of certain polyurethanes as coatings as disclosed in U.S. Pat.No. 5,110,666 to Menzel et al. (herein incorporated by reference)permits low add on weights reported to be in the range of 0.1 to 1ounces per square yard but the material itself is relatively expensiveand is believed to require relatively complex compounding andapplication procedures due to the nature of the coating materials.Patentees, however, fail to disclose any pertinent elasticity and/ortensile strength characteristics of their particular polyurethanecoating materials. Furthermore, there is no discussion pertaining to theimportance of the coating ability (and thus correlated low airpermeability) at low add-on weights of such polyurethane materials onside curtain airbags only for fabrics which are utilized within driveror passenger side cushions. All airbags must be inflatable extremelyquickly; upon sensing a collision, in fact, airbags usually reach peakpressures within 10 to 20 milliseconds. Regular driver side andpassenger side air bags are designed to withstand this enormousinflation pressure; however, they also deflate very quickly in order toeffectively absorb the energy from the vehicle occupant hitting the bag.Such driver and passenger side cushions (airbags) are thus made from lowpermeability fabric, but they also deflate quickly at connecting seams(which are not coated to prevent air leakage) or through vent holes.Furthermore, the low add-on coatings taught within Menzel, and withinU.S. Pat. No. 5,945,186 to Li et al., would not provide long-term gasretention; they would actually not withstand the prolonged andcontinuous pressures supplied by activated inflators for more than about2 seconds, at the most. The low permeability of these airbag fabricsthus aid in providing a small degree of sustained gas retention withindriver and passenger airbag cushions to provide the deflating cushioningeffects necessary for sufficient collision protection. Such airbagfabrics would not function well as side curtain airbags, since, at thevery least, the connecting seams which create the pillowed, cushionedstructures within such airbags, as discussed in greater detail below,would not be coated. As these areas provide the greatest degree ofleakage during and after inflation, the aforementioned patentedlow-coating low-permeability airbag fabrics would not be properlyutilized within side curtain airbags. Lastly, polyurethanes suffer fromaging and durability problems which requires complexities of mixing andapplication to overcome such difficulties.

As alluded to above, there are three primary types of different airbags,each for different end uses. For example, driver-side airbags aregenerally mounted within steering columns and exhibit relatively highair permeabilities in order to act more as a cushion for the driver uponimpact. Passenger-side airbags also comprise relatively high airpermeability fabrics which permit release of gas either therethrough orthrough vents integrated therein. Both of these types of airbags aredesigned to protect persons in sudden collisions and generally burst outof packing modules from either a steering column or dashboard (and thushave multiple “sides”). Side curtain airbags, however, have beendesigned primarily to protect passengers during rollover crashes byretaining its inflation state for a long duration (for example,exhibiting a retention of at least 50% of the initial pressure after 5seconds subsequent to high pressure inflation) and generally unroll frompacking containers stored within the roofline along the side windows ofan automobile (and thus have a back and front side only). Side curtainairbags therefore not only provide cushioning effects but also provideprotection from broken glass and other debris. As such, it is imperativethat side curtain airbags, as noted above, retain large amounts of gas,as well as high gas pressures, to remain inflated throughout the longertime periods of the entire potential rollover situation. To accomplishthis, these side curtains are generally coated with very large amountsof silicone sealing materials on both the front and back sides. Sincemost side curtain airbag fabrics comprise woven blanks that are sewn,sealed, or integrally woven together, discrete areas of potentially highleakage of gas are prevalent, particularly at and around the seams. Ithas been accepted as a requirement that heavy coatings were necessary toprovide the low permeability (and thus longer leak-down time) necessaryfor side curtain airbags. Without such heavy coatings, such airbagswould most likely deflate too quickly and thus would not functionproperly during a rollover collision. As will be well understood by oneof ordinary skill in this art, such heavy coatings add great cost to theoverall manufacture of the target side curtain airbags. There is thus agreat need to manufacture low permeability side curtain airbags withless expensive (preferably lower coating add-on weight) coatings withoutlosing the aging, humidity, and permeability characteristics necessaryfor proper functioning upon deployment. To date, there has been littleaccomplished, if anything at all, alleviating the need for such thickand heavy airbag coatings from side curtain airbags. Furthermore, sincesilicones (i.e., polyorganosiloxanes and the like) provide the bestoverall aging stability and durability performance as airbag coatings,there is a desire to utilize such beneficial types of materials for lowpermeability airbags. Unfortunately, to date the only teachingsregarding such silicone-based materials concern extremely thick, andthus costly and difficult to handle and apply, coating formulations. Aneed thus exists to provide lower add-on weights for silicone-basedairbag coating compositions, but with the same aging, durability, andlow permeability performance characteristics.

Furthermore, there is a current drive to store such low permeabilityside curtain airbags within cylindrically shaped modules. Since theseairbags are generally stored within the rooflines of automobiles, andthe area available is quite limited, there is always a great need torestrict the packing volume of such restraint cushions to their absoluteminimum. However, the previously practiced low permeability side curtainairbags have proven to be very cumbersome to store in such cylindricallyshaped containers at the target automobile's roofline. The actual timeand energy required to roll such heavily coated low permeabilityarticles as well as the packing volume itself, has been very difficultto reduce. Furthermore, with such heavy coatings utilized, the problemsof blocking (i.e., adhering together of the different coated portions ofthe cushion) are amplified when such articles are so closely packedtogether. The chances of delayed unrolling during inflation are raisedwhen the potential for blocking is present. Thus, a very closely packed,low packing volume, low blocking low permeability side curtain airbag ishighly desirable. Unfortunately, the prior art has again not accordedsuch an advancement to the airbag industry.

OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION

In light of the background above, it can be readily seen that thereexists a need for a low permeability, side curtain airbag that utilizeslower, and thus less expensive, amounts of durable, silicone-basedcoatings exhibiting good aging characteristics, and therefore exhibit asubstantially reduced packing volume over the standard low permeabilitytype side curtain airbags. Such a coated low permeability airbag mustprovide a necessarily high leak-down time upon inflation and afterlong-term storage. Such a novel airbag and a novel coating formulationprovides marked improvements over the more expensive, much higher add-onairbag coatings (and resultant airbag articles) utilized in the past.

It is therefore an object of this invention to provide a coated airbag,wherein the coating comprises a majority (at least) of siliconematerials, is present in a very low add-on weight, and possessesextremely high leak-down time characteristics after inflation and thuscomplementary low permeability characteristics. Another object of theinvention is to provide an inexpensive side curtain airbag cushion. Afurther object of this invention is to provide an highly effectiveairbag coating formulation which may be applied in very low add-onamounts to obtain extremely low permeability airbag structures afterinflation. An additional object of this invention is to provide anairbag coating formulation which not only provides beneficial andlong-term low permeability, but also exhibits excellent long-termstorage stability (through heat aging and humidity aging testing).

Accordingly, this invention is directed to an airbag cushion comprisinga coated fabric, wherein said fabric is coated with an elastomericcomposition in an amount of at most about 3.0 ounces per square yard,preferably, at most about 2.5 ounces per square yard of the fabric;wherein said elastomeric composition comprises at least 50% by weight ofthe entire composition of silicone-based materials; and wherein saidairbag cushion, after long-term storage, exhibits a characteristicleak-down rate of at least half of its initial inflation pressure (andthus upon retention of at least half of the inflation gas itself) of atleast 5 seconds, preferably higher than 10, and most preferably higherthan 50. Also, this invention concerns an airbag cushion comprising acoated fabric, wherein said fabric is coated with an elastomericcomposition comprising at least 50% by weight of the entire compositionof solvent-based silicone materials comprising from 10 to 90% solidscontent; and wherein said airbag cushion, after long-term storage,exhibits a characteristic leak-down rate of at least half of its initialinflation pressure (and thus upon retention of at least half of theinflation gas itself) of at least 5 seconds.

The term “characteristic leak-down rate” is intended to encompass themeasurement of time required for the pressure within a target coatedairbag to be reduced from an inflation pressure to half of its initialinflation pressure, for example from about 30 psi to 15 psi, or fromabout 15 to about 7 psi, due to escape of inflation gas through openingswithin the airbag and within the coating which develop upon exposure tosuch high pressures. Thus, this measurement begins the instant afterpeak initial pressure is reached upon inflation (such as, traditionally,about 30 psi, or as low as 7 psi) with a standard inflation module whichcontinues to pump gas into the target airbag during and after peakinitial pressure is reached. It is well understood that the pressure ofgas forced into the airbag after peak initial pressure is reached willnot remain stable (it decreases during the subsequent introduction ofinflation gas), and that the target airbag will inevitably permit escapeof a certain amount of inflation gas during that time. The primary focusof such side curtain airbags (as noted above) is to remain inflated foras long as possible in order to provide sufficient cushioning protectionto vehicle occupants during rollover accidents. The greater amount ofgas retained, the better cushioning effects are provided the passengers.Thus, the longer the airbag retains a large amount of inflation gas, andconsequently the greater the characteristic leak-down time, the bettercushioning results are achieved. At the very least, the inventive airbagmust retain at least half of its inflated gas volume 7 secondssubsequent to reaching peak initial pressure.

In an alternative, such a term is also intended to encompass themeasurement of time required for the entire amount of inflation gasintroduced within an already-inflated (to a peak initial pressure which“opens” up the areas of weak sealing) and deflated airbag cushion uponsubsequent re-inflation at a constant pressure at 10 psi. It is wellknown and well understood within the airbag art, and particularlyconcerning side curtain (low permeability) airbag cushions, thatretention of inflation gas for long periods of time is of utmostimportance during a collision. Side curtain airbags are designed toinflate as quickly as driver- and passenger-side bags, but they mustdeflate very slowly to protect the occupants during roll over and sideimpact. Thus, it is imperative that the bag exhibit a very low leakagerate after the bag experiences peak pressure during the instantaneous,quick inflation. Hence, the coating on the bag must be strong enough towithstand the shock and stresses when the bag is inflated so quickly.Thus, a high characteristic leak-down time measurement is paramount inorder to retain the maximum amount of beneficial cushioning gas withinthe inflated airbag. Airbag leakage after inflation (and after peakpressure is reached) is therefore closely related to actual pressureretention characteristics. The pressure retention characteristics(hereinafter referred to as “leak-down time”) of already-inflated anddeflated side curtain airbags can be described by a characteristicleak-down time t, wherein:${t\quad ({second})} = {\frac{{Bag}\quad {volume}\quad \left( {ft}^{3} \right)}{{Volumetric}\quad {leakage}\quad {rate}\quad \left( {SCFM}^{*} \right)\quad {at}\quad 10\quad {Psi}} \times 60}$ ^(*)SCFM:  standard  cubic  feet  per  minute.  

It is understood that the 10 psi constant is not a limitation to theinvention; but merely the constant pressure at which certain leak-downtime measurements can be made. Thus, even if the pressure is above orbelow this amount during actual inflation or after initial pressurizingof the airbag, the only limitation is that if one of ordinary skill inthe art were to measure the bag volume and divide that by the volumetricleakage rate time (measured by the amount leaking out of the targetairbag during steady state inflation at 10 psi), the resultantmeasurement in time would be at least 10 seconds at a coating add-onweight of about 1.5 ounces per square yard. Preferably, this time isgreater than about 10 seconds; more preferably, greater than about 20seconds; still more preferably in excess of about 40 seconds; and mostpreferably, greater than about 50 seconds.

Likewise, the term, “after long-term storage” encompasses either theactual storage of an inventive airbag cushion within an inflatorassembly (module) within an automobile, and/or in a storage facilityawaiting installation. Such a measurement is generally accepted, and iswell understood and appreciated by the ordinarily skilled artisan, to bemade through comparable analysis after representative heat and humidityaging tests. These tests generally involve 120° C. oven aging for 14days, or, alternatively, but comparably, oven aging at 80° C. and 95%relative humidity aging for 14 days. Such tests are universally acceptedas proper estimations of the conditions of long-term storage for airbagcushions. Thus, this term encompasses such measurement tests. Theinventive airbag fabrics must exhibit proper characteristic leak-downtimes after undergoing such rigorous pseudo-storage testing.

The inventive coating composition must comprise at least 50% by weightof at least one silicone-based elastomer and such a composition may onlybe present on the target airbag surface in an amount of at most 3.0ounces per square yard of fabric. Preferably, this amount ranges fromabout 0.5 to about 2.5 ounces per square more preferably from about 1.0to about 2.0; and most preferably from about 1.5 to about 2.0.Furthermore, the silicone-based elastomer preferably comprises at least60% by weight of the entire composition, more preferably at least about75%, yet more preferably at least 90%, and most preferably, at least 95up to 100%.

The term silicone-based materials or elastomers is intended to encompassany compound comprising silicone bonded with at least one oxygen atom(such as, for example, polyorganosiloxanes). Preferred compounds of thistype are listed below.

It is this high amount of silicone-based materials with acorrespondingly low add-on weight and resultant high leak-down time(provided for the target airbag fabric) which is of greatest importanceand which is so highly unexpected within this invention. As noted above,the utilization of silicone-based materials has been of great desirewithin low-permeability airbag articles; however, due to low elongationand tensile strength characteristics, the coatings required to providethe desired low permeability measurements were too thick (and tooexpensive) to provide a viable coating within the industry. The abilityto provide silicone-based coatings with substantially uniform coatingthicknesses (with extremely low thickness variations) has created theopportunity now to utilize the desired silicones as the prominentcoating materials within these specific low-permeability applications.

Thus, the silicones within the inventive coatings are preferablysolvent-based and exhibit a solids content of between about 10 and 90%of the total silicone composition. Preferably, this amount is from about20 to about 80%; more preferably from about 30 to about 75%; and mostpreferably from about 35 to about 65%. The solids content permitsgreater control of application on the target fabric surface. Generally,a dry coating is ineffective and an overly liquid composition (althougheasier to handle on an industrial scale initially) effectively preventsa low variation (in terms of thickness) coating to be applied over thetarget fabric surface. It has now been found that silicone-basedmaterials will provide the desired high elongation at break and tensilestrength characteristics if the coating applied to the target fabricsurface does indeed exhibit a substantially uniform thickness. Since thecoating must fill the interstitial spaces between yarns and seams, themore uneven the coating in such discrete areas, the easier it is todisplace it. A more balanced, and thus stronger, coating, thus providesthe needed ability to retain the greatest amount of coating over itsapplied area during an inflation event for the longest amount of time.Thus, the specific silicone-based coating composition herein discussedmust be in contact with the target fabric surface. It may be treatedwith other materials to aid in blocking reduction (i.e., adhesionbetween folded portions of coated fabric), greater aging stability, andmoisture resistance, if desired.

In the past, knife coating (including knife-over-gap) was the primarymethod of applying silicone-based materials to airbag surfaces. However,due to the physical state of such traditional materials (i.e., lowsolids content), the applied coating was extremely difficult to apply ina uniform fashion (with respect to coating thickness). It has now beenfound that the utilization of the higher solids content silicone-basedmaterials noted above, the application method may be followed with, forexample, a wider gap during the knife coating, permitting greatercontrol (and less “smearing”) of the applied coating to effectuate thedesired substantially uniform, low add-on, level.

Hence, with a substantially uniform, low add-on thickness, thesilicone-based coating exhibits the desired high levels of tensilestrength of at least 1,000 psi (preferably, at least 1,100, morepreferably at least 1,200, and most preferably at least 1,250) and anelongation to break of greater than about 200% (preferably in excess ofabout 300%, more preferably greater than 500%, and most preferablygreater than about 600%). These characteristics of the elastomertranslate to a coating that is both very strong (and thus will withstandenormous pressures both at inflation and during the time after inflationand will not easily break) and can stretch to compensate for such largeinflation, etc., pressures. Thus, when applied at the seams of a sidecurtain airbag, as well as over the rest of the airbag structure, thecoating will most preferably (though not necessarily) form a continuousfilm. This coating acts to both fill the individual holes between thewoven yarns and/or stitches, etc., as well as to “cement” the individualyarns in place. During inflation, then, the coating prevents leakagethrough the interstitial spaces between the yarns and aids in preventingyarn shifting (which may create larger spaces for possible gas escape).

Synergistically, the availability of such high tensile strength and highelongation at break silicone-based materials permits the consequentutilization, surprisingly, of extremely low add-on weight amounts ofsuch highly desirable coating formulations (as noted previously).Normally, the required coatings on side curtain airbags are very high,at least 3.0 ounces per square yard (with the standard actually muchhigher than that, at about 4.0). The inventive airbag cushions requiremuch less coating amounts (in terms of add-on weights on the targetfabric) to achieve the desired leak down rate. The inventive coatingsare present preferably in an amount of about at most 3.0 (preferablyless, such as 2.0, more preferably 1.8, still more preferably, about1.5, and most preferably, as low as 0.8) ounces per square yard toeffectuate the desired high leak-down (low permeability). Furthermore,such silicone-based coatings exhibit excellent heat and humidity agingstability. Thus, the coating compositions and coated airbags are clearlyimprovements within this specific airbag art.

Examples of silicone-based materials and/or elastomers acceptable forutilization within this invention by exhibiting the proper ability toform a substantially uniformly thick permeability controlling coating ona target airbag fabric surface include such beneficial solids contentcompositions as Rhodia® HS-60, available from Rhodia, Inc. andpossessing a solids content of about 50%, and Dow-Coming TR-55 siliconesexhibiting solids content measurements of about 30%, both in relation tothe total solvent-based compositions. The solvents present within thepotential high solids content compositions may be any standard organicliquid solvents, such as lower alcohols (isopropanol, ethanol, butanol,and the like), aromatic liquids, such as toluene, aniline, and the like,methyl ethyl ketone, and any other such standard solvents.

Other possible components present within the elastomer coatingcomposition are viscosity modifying agents, antioxidants, flameretardants, coalescent agents, adhesion promoters, and colorants.

Primer adhesives may be utilized to facilitate adhesion between thesurface of the target fabric and the elastomer itself. Thus, although itis preferable for the elastomer to be the sole component of the entireelastomer composition in contact with the fabric surface, it is possibleto utilize adhesion promoters, such as isocyanates, epoxies, functionalsilanes, and other such resins with adhesive properties, withoutdeleteriously effecting the ability of the elastomer to provide thedesired low permeability for the target airbag cushion. An overtreatmentcomponent, as noted above, may also be utilized to effectuate propernon-blocking characteristics to the target airbag cushion. Such atreatment may perform various functions, including, but not limited to,improving aging of the elastomer (such as with silicone) or providingblocking resistance due to the adhesive nature of the coating materials.

Airbag fabrics must pass certain tests in order to be utilized withinrestraint systems. One such test is called a blocking test whichindicates the force required to separate two portions of coated fabricfrom one another after prolonged storage in contact with each other(such as an airbag is stored). Laboratory analysis for blocking entailspressing together coated sides of two 2 inch by 2 inch swatches ofairbag fabric at 5 psi at 100° C. for 7 days. If the force required topull the two swatches apart after this time is greater than 50 grams, orthe time required to separate the fabrics utilizing a 50 gram weightsuspended from the bottom fabric layer is greater than 10 seconds, thecoating fails the blocking test. Clearly, the lower the requiredseparating shear force, the more favorable-the coating. For improvedblocking resistance (and thus the reduced chance of improper adhesionbetween the packed fabric portions), topcoat components may be utilized,such as talc, silica, silicate clays, and starch powders, as long as theadd-on weight of the entire elastomer composition (including thetopcoat) does not exceed about 3.0 ounces per square yard, preferablyabout 3.0 ounces per square yard (and preferably exists at a much lowerlevel, about 2.0, for instance). Preferably, talc is the utilizedtopcoat (if one is present at all). Other potential topcoats (thoughmuch less desired) include, polyamides, NBR rubbers, EPDM rubbers, andthe like, as long as the elastomer composition (including the topcoat)does not exceed the 3.0 ounces per square yard of the add-on weight tothe target fabric.

Two other tests which the specific coated airbag cushion must pass arethe oven (heat) aging and humidity aging tests. Such tests also simulatethe storage of an airbag fabric over a long period of time upon exposureat high temperatures and at relatively high humidities. These tests areactually used to analyze alterations of various different fabricproperties after such a prolonged storage in a hot ventilated oven(>100° C.) (with or without humid conditions) for 2 or more weeks. Forthe purposes of this invention, this test was used basically to analyzethe air permeability of the coated side curtain airbag by measuring thecharacteristic leak-down time (as discussed above, in detail). Theinitially produced and stored inventive airbag cushion should exhibit acharacteristic leak-down rate of half of its initial inflation pressureof at least 5 seconds, and preferably much higher. Alternatively, acharacteristic leak-down time of greater than about 5 seconds (uponre-inflation at 10 psi gas pressure after the bag had previously beeninflated to a peak pressure above about 15 psi and allowed to fullydeflate) under such harsh storage conditions. Other additives may bepresent within the elastomer composition, including, and not limited to,UV stabilizers, fillers, pigments, and crosslinking/curing agents, asare well known within this art.

The substrate to which the inventive high solids content silicone-basedelastomeric coatings are applied to form the airbag base fabric inaccordance with the present invention is preferably a woven fabricformed from yarns comprising synthetic fibers, such as polyamides orpolyesters. Such yarn preferably has a linear density of about 105denier to about 840 denier, more preferably from about 210 to about 630denier, and most preferably from about 315 to about 420 denier. Suchyarns are preferably formed from multiple filaments wherein thefilaments have linear densities of about 6 denier per filaments or lessand most preferably about 4 denier per filament or less. In the morepreferred embodiment such substrate fabric will be formed from fibers ofnylon, and most preferred is nylon 6,6. It has been found that suchpolyamide materials exhibit particularly good adhesion and maintenanceof resistance to hydrolysis when used in combination with the coatingaccording to the present invention. Such substrate fabrics arepreferably woven using fluid jet weaving machines as disclosed in U.S.Pat. Nos. 5,503,197 and 5,421,378 to Bower et al. (incorporated hereinby reference). Such woven fabric will be hereinafter referred to as anairbag base fabric. As noted above, the inventive airbag must exhibitextremely low permeability and thus must be what is termed a “sidecurtain” airbag. As noted previously and extensively, such side curtainairbags (a.k.a., cushions) must retain a large amount of inflation gasduring a collision in order to accord proper long-duration cushioningprotection to passengers during rollover accidents. Any standard sidecurtain airbag may be utilized in combination with the low add-oncoating to provide a product which exhibits the desired leak-down timesas noted above. Most side curtain airbags are produced throughlabor-intensive sewing or stitching (or other manner) together twoseparate woven fabric blanks to form an inflatable structure.Furthermore, as is well understood by the ordinarily skilled artisan,such sewing, etc., is performed in strategic locations to form seams(connection points between fabric layers) which in turn produce discreteopen areas into which inflation gasses may flow during inflation. Suchopen areas thus produce pillowed structures within the final inflatedairbag cushion to provide more surface area during a collision, as wellas provide strength to the bag itself in order to withstand the veryhigh initial inflation pressures (and thus not explode during such aninflation event). Other side curtain airbag cushions exist which are ofthe one-piece woven variety. Basically, some inflatable airbags areproduced through the simultaneous weaving of two separate layers offabric which are joined together at certain strategic locations (again,to form the desired pillowed structures). Such cushions thus presentseams of connection between the two layers. It is the presence of somany seams (in both multiple-piece and one-piece woven bags) whichcreate the aforementioned problems of gas loss during and afterinflation. The possibility of yarn shifting, particularly where theyarns shift in and at many different ways and amounts, thus creates thequick deflation of the bag through quick escaping of inflation gasses.Thus, the base airbag fabrics do not provide much help in reducingpermeability (and correlated leak-down times, particularly at relativelyhigh pressures). It is this seam problem which has primarily created theneed for the utilization of very thick, and thus expensive, coatings toprovide necessarily low permeability in the past.

Recently, a move has been made away from both the multiple-piece sidecurtain airbags (which require great amounts of labor-intensive sewingto attached woven fabric blanks) and the traditionally producedone-piece woven cushions, to more specific one-piece woven fabrics whichexhibit substantially reduced floats between woven yarns tosubstantially reduce the unbalanced shifting of yarns upon inflation,such as in Ser. No. 09/406,264, to Sollars, Jr., now U.S. Pat. No.6,220,309, the specification of which is completely incorporated herein.These one-piece woven bags are generally produced on dobby or jacquardfluid-jet looms, preferably the utilized one-piece airbag is made from ajacquard weaving process. With such an improvement, the possibility ofhigh leakage at the seams is substantially reduced. These airbagsprovide balanced weave constructions at and around attachment pointsbetween two layers of fabrics such that the ability of the yarns tobecome displaced upon inflation at high pressures is reduced as comparedwith the standard one-piece woven airbags (basically, the floats withinthe woven seams forming the inflation chambers of such cushions numberat most 3 picks in order to provide such desired low permeabilitycharacteristics). Unfortunately, such inventive one-piece woven bags arestill problematic in that the weave intersections may be displaced uponhigh pressure inflation such that leakage will still most likely occurat too high a rate for proper functioning. As a result, there is still aneed to coat such one-piece woven structures with materials which reduceand/or eliminate such an effect. However, such one-piece wovenstructures permit extremely low add-on amounts of elastomeric coatingsfor low permeability 2.0 and al low as about 1.0 ounces per square yard.

Furthermore, although it is not preferred in this invention, it has beenfound that the inventive coating composition provides similar lowpermeability benefits to standard one-piece woven airbags, particularlywith the inventive low add-on amounts of high tensile strength, highelongation, silicone-based elastomer materials; however, the amount ofcoating required to permit high leak-down times is much higher than forthe aforementioned Sollars, Jr. inventive one-piece woven structure.Thus, add-on amounts of as much as 1.5 and even up to about 2.5 ouncesper square yard may be necessary to effectuate the desired low level ofair permeability for these other one-piece woven airbags. Even with suchhigher add-on coatings, the inventive coatings themselves clearlyprovide a marked improvement over the standard, commercial, prior artsilicone, etc., coatings (which must be present in amounts in excess of3.0 ounces per square yard).

Additionally, it has also been found that the inventive coatingcompositions, at the inventive add-on amounts, etc., provide the sametypes of benefits with the aforementioned sewn, stitched, etc., sidecurtain airbags. Although such structures are highly undesirable due tothe high potential for leakage at these attachment seams, it has beenfound that the inventive coating provides a substantial reduction inpermeability with correlative lower add-on amounts than with standardlow permeability, high add-on silicone and neoprene rubber coatingformulations. Such add-on amounts for the inventive coatings willapproach the 3.0 ounces per square yard, but lower amounts have proveneffective (lower than 2.5, lower than 2.0, and most preferably less thanabout 1.5 ounces per square yard, for example) depending on theutilization of a sufficiently high tensile strength and sufficientlystretchable elastomeric component within the coating compositiondirectly in contact with the target fabric surface. Again, with theability to reduce the amount of coating materials (which are generallyalways quite expensive), while simultaneously providing a substantialreduction in permeability to the target airbag structure, as well ashigh resistance to humidity and extremely effective aging stability, theinventive coating composition, and the inventive coated airbag itself isclearly a vast improvement over the prior airbag coating art.

Of particular importance within this invention is the ability to packthe coated airbag cushions within cylindrical storage containers at theroof line of a target automobile in as small a volume as possible. In arolled configuration (in order to best fit within the cylindricalcontainer itself, and thus in order to best inflate upon a collisionevent downward to accord the passengers sufficient protection), theinventive airbag may be constricted to a cylindrical shape having adiameter of at most 23 millimeters. In such an instance, with a 2 meterlong cylindrical roofline storage container, the necessary volume ofsuch a container would equal about 830 cm³.(with the volume calculatedas 2[Pi]radius²) Standard rolled packing diameters are at least 25millimeters for commercially available side curtain airbag cushions (dueto the thickness of the required coating to provide low permeabilitycharacteristics). Thus, the required cylindrical container volume wouldbe at least 980 cm³. Preferably, the rolled diameter of the inventiveairbag cushion during storage is at most 20 millimeters (giving a packedvolume of about 628 cm³) which is clearly well below the standardpacking volume. In relation, then, to the depth of the airbag cushionupon inflation (i.e., the length the airbag extends from the rooflinedown to its lowest point along the side of the target automobile, suchas at the windows), the quotient of the inventive airbag cushion's depth(which is standard at approximately 17 inches or 431.8 millimeters) toits rolled packed diameter should be at least about 18.8. Preferablythis quotient should be about 21.6 (20 millimeter diameter), and, at itsmaximum, should be about 24 (with a minimum diameter of about 18millimeters). Of course, this range of quotients does not require thedepth to be at a standard of 17 inches, and is primarily a function ofcoating thickness, and thus add-on weight.

The inventive coatings are preferably knife-over-gap coated across thefabric substrate and dried and cured to form the necessarily thin,substantially uniform coating. Other controlled thickness coatingmethods can be utilized, including, without limitation, floating knife,and knife-over-foam pad methods, to name a few different method types.Particularly preferred, however, is fixed-gap knife coating in order toprovide a uniform coating (or possibly film) on the target fabricsurface. A fixed-gap coating procedure which permits even coating overthe raised yarns of the target fabric is highly desired. The final dryweight of the coating is preferably from about 0.5-3.0, more preferablyfrom 1.0-2.5 ounces per square yard or less and most preferably 1.5-2.25ounces per square yard or less. The resultant airbag cushion issubstantially impermeable to air when measured according to ASTM TestD737, “Air Permeability of Textile Fabrics,” standards.

While the invention will be described and disclosed in connection withcertain preferred embodiments and practices, it is in no way intended tolimit the invention to those specific embodiments, rather it is intendedto cover equivalent structures structural equivalents and allalternative embodiments and modifications as may be defined by the scopeof the appended claims and equivalence thereto.

PREFERRED EMBODIMENTS OF THE INVENTION

In order to further describe the present invention the followingnonlimiting examples are set forth. These examples are provided for thesole purpose of illustrating some preferred embodiments of the inventionand are not to be construed as limiting the scope of the invention inany manner.

Some other silicone-based elastomers potentially preferred within thisinvention include:

TABLE 1 Other Preferred Silicone-Based Coating Materials TensileElongation Tear Spec. Commercial name Strength at Break Strength GravityRhodia ® 50042  800 psi 920% 125 ppi 1.12 Rhodia ® 50065 1100 psi 1000% 200 ppi 1.12 Rhodia ® 50066 1100 psi 900% 220 ppi 1.13 Rhodia ® 500671100 psi 700% 270 ppi 1.14 Rhodia ® 50069 1150 psi 700% 290 ppi 1.14Rhodia ® 50081 1250 psi 700% 300 ppi 1.15 Rhodia ® 50071 1000 psi 450%200 ppi 1.18 Dow Corning ® 4-7224 1220 psi 744%  80 ppi * Dow Corning ®94-595 1600 psi 600%  80 ppi * Dow Corning ® TR-55 1488 psi 791%  24 ppi*

Specific compounding and application to target fabric of the inventivesilicone-based materials was undertaken as follows:

EXAMPLE 1

The following coating formulation was first compounded:

Component Amount Rhodia ® HS-60 Part A Silicone  50 parts Rhodia ® HS-60Part B Silicone  50 parts Toluene 100 parts

This fomulation was prepared and applied to a one-piece wovenside-curtain airbag made from 420 denier nylon 6,6 yarns and includingwoven-in seams exhibiting no more than 3 sequential floats per pick (inaccordance with the preferred bag within U.S. patent application Ser.No. 09/406,264, to Sollars, Jr.

The solvent dispersion was applied to the bag with a knife over rollcoating method. The coating gap of 825 microns was used in order totarget a coating add-on of 2.0 oz/yd. The solvent was removed in thedrying oven and the fabric cured 180° C. for 2 minutes followed by apost cure of 7 minutes in a separate oven to ensure optimum cure. Theactual coating add-on was determined to be 1.78 oz/yd².

The test bag was then tested on a high pressure permeability tester byincrementally increasing the pressure up to a maximum of 15 psi. Theflow rates observed were as follows:

psi flow (scfm)  2.5 0.00  5.0 0.07  7.5 0.09 10.0 0.13 12.5 0.17 15.00.28

After reaching 15 psi, the air supply valve was closed and the amount oftime to drop from the peak pressure of 15 psi to a pressure of 7 psi wasdetermined to be 33 seconds.

EXAMPLEs 2-4

The same coating formulation in EXAMPLE 1, above, was applied to threeseparate one-piece woven airbags (as above), but in different fabricadd-on weights. EXAMPLE 2 was applied in an amount of about 2.25 ouncesper square yard; EXAMPLE 3, about 1.90; and EXAMPLE 4 about 1.56. Theresults for each (leak-down rate) is tabulated below with a finalnotation showing the actual time required for the inventive airbags tolose inflation pressure to about half of its initial level.

Leak-Down Rate (SCFM at indicated pressure) Leak-Down Time EXAMPLE 10kPa 20 kPA 30 pKa 40 pKa 50 pKa 60 pKa 70 pKa (secs.) from 70 to 40 kPa2 0.0 0.0 0.09 0.09 0.13 0.13 0.22 163 3 0.0 0.0 0.07 0.11 0.15 0.240.42  52 4 0.0 0.5 0.11 0.16 0.28 0.46 0.78  25

Thus, the inventive low add-on silicone-based coatings providedexcellent long-term low permeability to the target airbags.

DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the side, inside view of a vehicle prior to deployment ofthe inventive side curtain airbag.

FIG. 2 depicts the side, inside view of a vehicle after deployment ofthe inventive side curtain airbag.

FIG. 3 depicts a side view of a side curtain airbag.

FIG. 4 provides a side view of a side curtain airbag container.

FIG. 5 provides a cross-sectional perspective of the stored airbagwithin the container of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

As depicted in FIG. 1, an interior of a vehicle 10 prior to inflation ofa side curtain airbag (not illustrated) is shown. The vehicle 10includes a front seat 12 and a back seat 14, a front side window 16 anda back-side window 18, a roofline 20, within which is stored acylindrically shaped container 22 comprising the inventive side curtainairbag (not illustrated). Also present within the roofline 20 is aninflator assembly 24 which ignites and forces gas into the side curtainairbag (26 of FIG. 2) upon a collision event.

FIG. 2 shows the inflated side curtain airbag 26. As noted above, theairbag 26 is coated with at most 2.5 ounces per square of a coatingformulation (not illustrated), preferably the composition of EXAMPLE 1,above. The inventive airbag 26 will remain sufficiently inflated for atleast 5 seconds, and preferably more, such as from at least 20 to atleast 50 seconds, most preferably.

FIG. 3 shows the side curtain airbag 26 prior to storage in itsuninflated state within the roofline cylindrically shaped container 22.The thickness of the airbag 26, measured as the rolled packing diameter(as in FIG. 5, below) as compared with the depth of the airbag measuredfrom the roofline cylindrically shaped container 22 to the bottom mostpoint 28 of the airbag 26 either in its uninflated or inflated statewill be at least 17 and at most 29, as noted above.

FIGS. 4 and 5 aid in understanding this concept through the viewing ofthe rolled airbag 26 as stored within the container 22 along line 2. Thediameter measurement of the airbag 26 of Example 3, above, is roughly 20millimeters. The standard depth of side curtain airbags is roughly 17inches, or about 431.8 millimeters. Thus, the preferred packing volumefactor is about 21.6. A comparative silicone-based thick coating add-onweight of about 4.0 ounces per square yard provided a diameter of about25 millimeters for a factor of about 17.3.

There are, of course, many alternative embodiments and modifications ofthe present invention which are intended to be included within thespirit and scope of the following claims.

What is claimed is:
 1. An airbag cushion comprising a coated fabricwherein said fabric is coated with an elastomeric composition in anamount of at most about 3.0 ounces per square yard; wherein saidelastomeric composition comprises at least 90% by weight of the entirecomposition of silicone-based materials; and wherein said silicone-basedelastomeric composition is in contact with the surface of said airbagfabric.
 2. The airbag cushion of claim 1 wherein said airbag cushion,after long-term storage, exhibits a characteristic leak-down rate of atleast half of its initial inflation pressure of at least 5 seconds. 3.The airbag cushion of claim 1 wherein said coated fabric comprisesfibers selected from the group consisting of polyester and polyamide. 4.The airbag cushion of claim 3 wherein said coated fabric comprisespolyamide fibers selected from the group consisting of nylon 6 and nylon6,6.
 5. The airbag cushion of claim 4 wherein said fibers possessaverage deniers in the range of from 315 to about
 630. 6. The airbagcushion of claim 5 wherein said fibers possess average deniers of about420.
 7. The airbag cushion of claim 6 wherein said fibers are polyamidefibers selected from the group consisting of nylon 6 and nylon 6,6. 8.The airbag cushion of claim 1 wherein said airbag coating compositioncomprises at least 95% by weight of the total composition ofsilicone-based materials and is present on said airbag fabric in anamount of from about 1.5 to about 2.25 ounces per square yard of fabric.9. The airbag cushion of claim 2 wherein said coated fabric comprisesfibers selected from the group consisting of polyester and polyamide.10. The airbag cushion of claim 9 wherein said coated fabric comprisespolyamide fibers selected from the group consisting of nylon 6 and nylon6,6.
 11. The airbag cushion of claim 10 wherein said fibers possessaverage deniers in the range of from 315 to about
 630. 12. The airbagcushion of claim 11 wherein said fibers possess average deniers of about420.
 13. The airbag cushion of claim 12 wherein said fibers arepolyamide fibers selected from the group consisting of nylon 6 and nylon6,6.
 14. The airbag cushion of claim 2 wherein the characteristicleak-down rate is at least 10 seconds.
 15. The airbag cushion of claim14 wherein the characteristic leak-down rate is at least 20 seconds. 16.The airbag cushion of claim 15 wherein the characteristic leak-down rateis at least 30 seconds.
 17. The airbag cushion of claim 16 wherein thecharacteristic leak-down rate is at least 50 seconds.
 18. The airbagcushion of claim 1 wherein said cushion is a one-piece jacquard wovenside-curtain airbag exhibiting floats of at most 3 picks present withineach seam surrounding the inflated chamber.
 19. An airbag cushioncomprising a coated fabric, wherein said fabric is coated with anelastomeric composition comprising at least 90% by weight of the entirecomposition of solvent-based silicone materials comprising from 10 to90% solids content; wherein said airbag cushion, after long-termstorage, exhibits a characteristic leak-down rate to at least half ofits initial inflation pressure of at least about 5 seconds.
 20. Theairbag cushion of claim 19 wherein said coated fabric comprises fibersselected from the group consisting of polyester and polyamide.
 21. Theairbag cushion of claim 20 wherein said coated fabric comprisespolyamide fibers selected from the group consisting of nylon 6 and nylon6,6.
 22. The airbag cushion of claim 21 wherein said fibers possessaverage deniers in the range of from 315 to about
 630. 23. The airbagcushion of claim 22 wherein said fibers possess average deniers of about420.
 24. The airbag cushion of claim 23 wherein said fibers arepolyamide fibers selected from the group consisting of nylon 6 and nylon6,6.
 25. The airbag cushion of claim 19 wherein said airbag coatingcomposition comprises at least 95% by weight of the total composition ofsilicone-based materials and is present on said airbag fabric in anamount of from about 1.5 to about 2.25 ounces per square yard of fabric.26. The airbag cushion of claim 25 wherein said coated fabric comprisesfibers selected from the group consisting of polyester and polyamide.27. The airbag cushion of claim 26 wherein said coated fabric comprisespolyamide fibers selected from the group consisting of nylon 6 and 6,6.28. The airbag cushion of claim 27 wherein said fibers possess averagedeniers in the range of from 315 to about
 630. 29. The airbag cushion ofclaim 28 wherein said fibers possess average deniers of about
 420. 30.The airbag cushion of claim 29 wherein said fibers are polyamide fibersselected from the group consisting of nylon 6 and nylon 6,6.